1. Field
Apparatuses and methods consistent with what is disclosed herein relate to a transmitter, a receiver, and a controlling method thereof, and more specifically, to a transmitter configured to use an orthogonal frequency division multiplexing (OFDM) method, a receiver and a controlling method thereof.
2. Description of the Related Art
Recent broadcasting communication services are developing to be multi-functional using a high-quality broadband. Specifically, according to the development of the electronic technology, mobile broadcasting devices such as high-definition digital TV and high-performance smart phone are widely distributed. Thus, requests for various broadcasting services are growing.
For one example to follow these requests, broadcasting communication standards such as Digital Video Broadcasting the Second Generation Terrestrial (DVB-T2) are developing. DVB-T2 is the second generation European ground wave digital broadcasting standard which advances performance of DVB-T. DVB-T is selected to be a broadcasting standard in more than 35 countries in the world including Europe. DVB-T2 implements increasing of a transmitting amount and higher bandwidth efficiency by applying the latest technologies such as Low Density Parity Check (LDPC) codes and 256-QAM modulating method. Thereby, it has an advantage that high-quality of various services such as high-definition television (HDTV) can be provided within a limited bandwidth.
However, an OFDM system used in DVB-T2 may have a problem in which a high peak to average power ratio (PAPR) is generated due to modulation of multi-carrier waves. Thus, because the OFDM method transmits data by using multi-carrier waves, a size of the amplitude of final OFDM signals may be a sum of amplitude value of each carrier wave. Thus, the final OFDM signal may have great changes in the amplitude, or may have an extremely great value when phases of carrier waves are uniform to one another. Such high PAPR signals may be out of a linear operating range of a high power amplifier. Further, there may be a problem in which a system performance deteriorates by generating distortion in signals passing through the high power amplifier.
Various methods are being suggested in order to address the above problem regarding the PAPR of the OFDM system. There are various PAPR reducing methods such as a clipping method, coding, selected mapping (SLM), a partial transmit sequence (PTS), and tone injection (TI).
In the TI method which is one of the above PAPR reducing methods, an L number of tones are reserved among an N number of sub-carriers, and the L number of the reserved tones are used to reduce the PAPR without transmitting data.
FIG. 1 illustrates frame constitution regarding the related broadcasting communication system. A plurality of OFDM symbols constitute one frame, and the structure of pilots shows scattered constitution in which positions of the pilots change per OFDM symbol. Because the pilots are used to estimate channels, there should be no interference and distortion. However, when the above reserved tones are used, a problem occurs, in which the reserved tones collide with the pilots in the frame constitution of FIG. 1.
FIG. 2 illustrates a case in which collision between the pilots and the reserved tone occurs according to the method using reserved tones among the related tone reserving methods in the frame constitution of FIG. 1. Thus, 201 does not show collision between the reserved tone and the pilots. However, 202, 203, 204 do show a collision between the pilots and the reserved tone.
Thus, it is necessary to insert the reserved tones while avoiding collision between the pilots and the reserved tones increases.